This paper reports the latest attempt to model the creep deformation and rupture for high Cr (91) alloy under low stress range. While accurately predicting the creep deformation and damage and the ultimate rupture is paramount important, both for the academic research and industrial applications, the current situation is unsatisfactory, particularly for the lower stress range. This paper systematically investigates the formulation as well as tentatively underlines the scientific reasons, to improve and accurately predict the creep deformation, creep damage and the ultimate rupture of P91 in the stress range of 80–125 MPa. This paper contributes to the knowledge on how to accurately model the creep deformation and damage for P91. Furthermore, it contributes to the methodology through the development of a generic model.